Abstract
BackgroundThe non-invasive assessment of airway inflammation is potentially advantageous in asthma management. Exhaled carbon monoxide (eCO) measurement is cheap and has been proposed to reflect airway inflammation and oxidative stress but current data are conflicting. The purpose of this meta-analysis is to determine whether eCO is elevated in asthmatics, is regulated by steroid treatment and reflects disease severity and control.MethodsA systematic search for English language articles published between 1997 and 2009 was performed using Medline, Embase and Cochrane databases. Observational studies comparing eCO in non-smoking asthmatics and healthy subjects or asthmatics before and after steroid treatment were included. Data were independently extracted by two investigators and analyzed to generate weighted mean differences using either a fixed or random effects meta-analysis depending upon the degree of heterogeneity.Results18 studies were included in the meta-analysis. The eCO level was significantly higher in asthmatics as compared to healthy subjects and in intermittent asthma as compared to persistent asthma. However, eCO could not distinguish between steroid-treated asthmatics and steroid-free patients nor separate controlled and partly-controlled asthma from uncontrolled asthma in cross-sectional studies. In contrast, eCO was significantly reduced following a course of corticosteroid treatment.ConclusionseCO is elevated in asthmatics but levels only partially reflect disease severity and control. eCO might be a potentially useful non-invasive biomarker of airway inflammation and oxidative stress in nonsmoking asthmatics.
Highlights
The non-invasive assessment of airway inflammation is potentially advantageous in asthma management
heme oxygenase (HO)-1 is present in alveolar macrophages; there is conflicting evidence as to whether HO-1 is expressed in the airway epithelium and whether HO-1 is up-regulated in asthmatics [9,37,38]
Our meta-analysis demonstrated that the Exhaled carbon monoxide (eCO) level in steroid-treated asthmatics was not significantly different from that in steroid-free subjects the average level of eCO is increased in steroid-free subjects
Summary
The non-invasive assessment of airway inflammation is potentially advantageous in asthma management. Exhaled carbon monoxide (eCO) measurement is cheap and has been proposed to reflect airway inflammation and oxidative stress but current data are conflicting. The purpose of this meta-analysis is to determine whether eCO is elevated in asthmatics, is regulated by steroid treatment and reflects disease severity and control. The assessment of airway inflammation is likely to play an important role in the future management of asthma. Much attention is paid to the non-invasive measurement of airway inflammation, such as induced sputum and of surrogates such as exhaled nitric oxide (eNO). The measurement of eNO is expensive, limiting its use in primary care and most specialist clinics
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